ABB CIRCUIT SHIELD 87T - Page 15

Transformer
Differential
Relay
IB
7.6
.
1.7
-
4
Page
15
3
.
BUILT
-
IN
TEST FUNCTION
A
built
-
in
test
function is
provided
for
convenience
in
running
a
test
on
the
relay
and
associated
trip
circuits
.
The
test
button
is
labelled
TRIP
,
and
depressing
the
button
will
cause
an
immediate
trip
.
tests
should be made
with
the
main circuit
de
-
energized
.
If
tests
must
be
CAUTION
:
made
on an
energized
circuit
,
take all
necessary
precautions
.
4
.
ACCEPTANCE
TESTS
and
adjust
the
operating
characteris
-
The
following
procedures
can
be used
to
verify
tics
of the
Type
87
T
relay
.
A
.
Minimum
Operating
Current
and
%
Differential
Tests
:
Connect
the
relay
in
the
test
circuit
shown
in
Figure
8
.
Apply
control
voltage
per
the
relay
’
s
rating
as
marked
on
the front
panel
.
Select and make
settings
from the
listing
in
Table
5
.
Minimum
Operating
Current
:
Increase
the
I
2
current
until
the
87
T
operates
.
(
11
=
0
)
Compare
with
the
expected
value from Table
5
.
Pifferential
Characteristic
:
Set
the
I
2
current
for
5.8
amps
.
Increase
the
I
1
current to
5.8
amps
.
The
87
T
output
contact
should
now
be
open
.
Reset
the
target
to
black
.
Increase
the
I
1
current
until
the
87
T
operates
.
The
I
1
current
should be
within
the
limits
shown
.
Remember
:
since
the
%
Differential
and
Minimum
Restraint
dials
are
continuously
adjustable
,
you may
trim their
positions
if
desired
to
obtain
more
precisely
the
required operating
values
.
Important
note
:
Some
commercial
test sets
that have
2
independent
sources
are
not
suitable
for
the
differential
test
shown above
because
there
is
a
phase
-
shift
between the
sources
.
If
you
are
using
such
a
set
,
then
an
alternative
test
for the
differential
element
using
a
single
source
is
as
follows
:
a
.
Connect
the
relay
as
shown
in
Figure
9
.
b
.
Set
%
Diff
dial
to
40
%
,
taps
to
3.6
A
.
c
.
Apply
7.2
A
test
current
.
The
relay
should
not
trip
.
d
.
Move
one
tap
pin
to
2.9
A
position
.
Apply
7.2
A
and then
rotate
the
%
Diff
dial counterclockwise
slowly
until
the
relay
trips
.
The
dial
position
should be
21
-
27
%
.
Suggested
Settings
for
the
Acceptance
Test
Table
5
:
(
D
)
(
R
)
Min
Restraint
Min
Operate
Lim
Differential
Test
Set
I
2
I
1
limits
I
2
%
Diff
Taps
2.9
A
2.9
A
2.9
A
1 5
%
2.3
0.75
0.75
0.75
1.0
A
1
.
0
A
1.0
A
5.8
A
5.8
A
5.8
A
6.4
6.9
A
7.5
A
8.4
A
25
%
1
.
5
7.0
40
%
1
.
0
7.8
The
suggested
settings
selected
for
Table
5
use
the
lowest
tap
value
(
2.9
A
)
to
minimize
the
currents
required
for the
tests
.
If
you
must
check the
values
to
be used
in
your
application
,
the
following
formulas
apply
:
1
.
Minimum
operating
current
:
Im
D
=
%
Diff
setting
,
R
=
Minimum
Restraint
Setting
Increase
the
test current to
one
input
of the
relay
.
The
relay
should
trip
within
+
/
-
15
%
of the value calculated
.
(
Trim
dial
position
as
rqd
.
)
(
D
/
(
100
+
D
)
x
R
x
T
tap
value
T
2
.
Differential
characteristic
:
apply
test currents
of
2
times
the
tap
value
to
each of
two current
inputs
.
The
output
contact
should
be
open
.
Increase
one
source
until
the
output
contact
closes
.
The
current at
which
the
contact
closes
should
be
within
+
/
-
5
%
of the value calculated
from
:
1
=
T
x
(
2
D
+
2
)
T
=
tap
of
"
increased
D
=
%
Diff
setting
.
source
Courtesy of NationalSwitchgear.com